WASHINGTON – President Donald Trump signed executive orders Tuesday to revive the controversial Dakota Access and Keystone XL oil pipelines, another step in his effort to dismantle former President Barack Obama's environmental legacy.

He also signed an executive order to expedite environmental reviews of other infrastructure projects, lamenting the existing "incredibly cumbersome, long, horrible permitting process."

"The regulatory process in this country has become a tangled-up mess," he said.

It remained unclear how Trump's order would expedite those environmental reviews. Many are statutory and the legislation that created them cannot be swept aside by an executive order. Indeed, Trump's order on the Dakota Access pipeline left some ambiguity. The executive order directs the Army Corps of Engineers to "review and approve in an expedited manner, to the extent permitted by law."

Trump said that both pipeline projects would be subject to renegotiation. His order for the Keystone XL project "invites" the company to "re-submit its application."

In an Oval Office signing before reporters, the president hinted at a possible new wrinkle. He said he would want any new projects to make use of American steel, though that requirement is not mentioned in his executive order.

"I am very insistent that if we're going to build pipelines in the United States, the pipe should be made in the United States," he told reporters.

Dakota Access Pipeline protesters are seen at the Oceti Sakowin campground near the town of Cannon Ball, North Dakota. Morton County Sheriff’s Department/Handout via REUTERS/File

The orders will likely have an immediate impact in North Dakota, where the pipeline company Energy Transfer Partners wants to complete the final 1,100-foot piece of the 1,172-mile pipeline route that runs under Lake Oahe. The pipeline would carry oil from the booming shale oil reserves in North Dakota to refineries and pipeline networks in Illinois.

The Standing Rock Sioux tribe and other Native American groups have been protesting the project, which they say would imperil their water supplies and disturb sacred burial and archaeological sites. The Army Corp of Engineers called a halt to the project in December to consider alternative routes.

The tribe is expected to return to court in a bid to block the project. Last week the tribe asked remaining protesters – about 500 to 700 of whom were still in the main camp near the pipeline site – to leave and return to their homes. The camp is in a flood plain, and heavy snow could pose dangers when it starts melting.

The executive order from Trump on the Keystone XL pipeline threatens to undo a major decision by Obama, who said the project would contribute to climate change because it would carry tar sands crude oil, which is especially greenhouse gas intensive because of the energy it takes to extract the thick crude. Obama's announcement followed a similar finding by the State Department, which has reviewed applications for cross-border pipelines.

TransCanada, the Calgary-based project owner, has said it would be interested in reviving the pipeline. But it was unclear what Trump's caution about renegotiation would mean for TransCanada's plans. Originally, TransCanada had planned to get about 65 percent of the steel pipe from U.S. manufacturers but other supplies from Canada.

On Tuesday, Trump said: "From now on, we're going to be making pipeline in the United States. We build the pipelines, we want to build the pipe. We're going to put a lot of workers, a lot of skilled workers, back to work. We will build our own pipeline, we will build our own pipes, like we used to in the old days."

Speaking to reporters Monday, White House press secretary Sean Spicer said the president supported energy projects "like Dakota and the Keystone Pipeline, areas that we can increase jobs, increase economic growth, and tap into America's energy supply more, that's something that he has been very clear about."

Referring to comments Trump has made during the campaign and after the election, Spicer said: "He was talking about that being a big priority. That's one of those ones where I think that the energy sector and our natural resources are an area where I think the president is very, very keen on making sure that we maximize our use of natural resources to America's benefit."

"It's good for economic growth, it's good for jobs, and it's good for American energy," Spicer added.

As news of the move surfaced Tuesday morning, oil industry officials hailed it as overdue.

"Making American energy great again starts with infrastructure projects like these that move resources safely and efficiently," said Stephen Brown, vice president of federal government affairs at Tesoro Companies.

"We are pleased to see the new direction being taken by this administration to recognize the importance of our nation's energy infrastructure by restoring the rule of law in the permitting process that's critical to pipelines and other infrastructure projects," said Jack Gerard, president of the American Petroleum Institute.

Many lawmakers, including House Speaker Paul Ryan, R-Wis., and Sen. Heidi Heitkamp, D-N.D., backed the president's bid to revive the pipelines.

Environmentalists, by contrast, vowed to continue to fight the two pipelines.

Greenpeace Executive Director Annie Leonard noted in a statement that a broad coalition of opponents – "indigenous communities, ranchers, farmers, and climate activists" – managed to block the projects in the past and would not give up now.

"We all saw the incredible strength and courage of the water protectors at Standing Rock, and the people around the world who stood with them in solidarity," she said. "We'll stand with them again if Trump tries to bring the Dakota Access Pipeline, or any other fossil fuel infrastructure project, back to life."

"We will resist this with all of our power, and we will continue to build the future the world wants to see," she added.

Bill McKibben, founder of the activist group 350.org, which has fought both the Keystone XL and Dakota Access pipelines, said the decision to allow the projects to move forward ignores the massive opposition expressed both through public protests and in comments to government agencies.

"The world's climate scientists and its Nobel laureates explained over and over why it was unwise and immoral," McKibben said in a statement. "In one of his first actions as president, Donald Trump ignores all that in his eagerness to serve the oil industry. It's a dark day for a reason, but we will continue to fight."

Americans have tended to favor the Keystone XL project even as Obama rejected it. According to an October 2015 Washington Post-ABC News poll, 55 percent wanted the next president to support building the Keystone oil pipeline, while 34 percent wanted the new leader to oppose it, with majorities of Republicans and independents supportive. Earlier Post-ABC surveys found that Americans widely expected the project to create a significant amount of jobs, but that they were divided on whether it would pose a significant environmental risk.